NGC 6540
It is often considered that this object is one of the two toughest on the Herschel 400 list of the Astronomical League. This challenged me to see if I could observe it with my lovely little 6 inch dob. On July 21/08, my little scope rose to the challenge. I was observing from one of the pads of the Godin/Newton observatory at Pearson College. The conditions weren't the best with the 85% Moon above the horizon. Still this highly obscured by dust, globular cluster did reveal itself. It is located in Sagittarius just north of the spout of the teapot.
It was a difficuly observation to be sure, but for being so low to the horizon and with the Moon actually above the horizon I expected it to be more difficult.
This is how I observed globular cluster with my 6 inch dob at 160X magnification.